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  <script>
    /* 
    1. const / let
    2. 解构赋值  
    */
    // let a = 3
    // a = 4

    const {c, a} = {a: 2, b: 3, c: 4}
    const [aa, bb] = [1, 3, 4]


    /* 
    字符串扩展
    对象扩展
    函数扩展
    数组扩展
    */
    'abcd'.includes('bcde')

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